Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as "spitting." The waste ink is collected at a spitting reservoir portion of the service station, known as a "spittoon." After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, spitting to clear the nozzles becomes even more important when using pigment-based inks, because the higher solids content contributes to the clogging problem more than the earlier dye-based inks.
In previous technology spittoons, most of the spit ink landed in the bottom of the spittoon. Some of the ink, however, ran down the walls of the spittoon tube or "chimney" under the force of gravity and into a reservoir, where many solvents evaporated. Sometimes the waste ink solidified before reaching the reservoir, forming stalagmites from ink deposits along the sides of the chimney. These ink stalagmites often grew and clogged the entrance to the spittoon. To avoid this phenomenon, conventional spittoons must be wide, often over 8 mm in width to handle a high solid-content ink. Since the conventional spittoons were located between the printzone and the other servicing components, this extra width increased the overall printer width, resulting in additional cost being added to the printer, in material, and shipping costs. Moreover, this greater printer width increased the overall printer size, yielding a larger "footprint," that is, a larger working space required to receive the printing mechanism, which was undesirable to many consumers.
As mentioned above, conventional spittoons were located between the printzone and the other servicing components, and to minimize the impact on printer width, the conventional spittoons were only wide enough to receive ink from one printhead at a time. Thus, the conventional spitting routine of a multi-pen unit first positioned one printhead over the spittoon for spitting, then the pen carriage moved the next pen over the spittoon for spitting, etc. Unfortunately, all this carriage motion not only slowed the spitting routine, but it was also noisy
Besides increasing the solid content, mutually-precipitating inks have been developed to enhance color contrasts. For example, one type of color ink causes black ink to precipitate out of solution. This precipitation rapidly fixes the black solids to the page, which prevents bleeding of the black solids into the color regions of the printed image. Unfortunately, if the mutually precipitating color and black inks are mixed together in a conventional spittoon, they do not flow toward a drain or absorbent material. Instead, once mixed, the black and color inks rapidly coagulate into a gel with some residual liquid.
Thus, the mixed black and color inks not only may exhibit a rapid solid build-up, but the liquid fraction may also tend to run and wick (flowing through capillary action) into undesirable locations. To resolve the mixing problem, some printers used two conventional stationary spittoons, one for the black ink and one for the color inks. Unfortunately, each of these dual spittoons must be wide enough to avoid clogging from stalagmites growing inwardly from the side walls of the spittoon chimney. Such a dual-spittoon design, with the spittoons located between the printhead and other servicing components, further increased the overall width and footprint of the printer. Furthermore, besides growing from the sides of the spittoon, the ink stalagmites sometimes grew upwardly from the bottom of the spittoon. To prevent these stalagmites from interfering with the printhead over time, the use of very deep spittoons was typically required, which could also increase the overall printer size.
Simultaneously wiping two or more printheads, one containing a pigment based ink and the other containing dye based ink, has also been a challenge. Simultaneous wiping speeds the servicing routine, so the pens can quickly return to printing. New wiping strategies are needed to accommodate the pigment based inks. To maintain the desired ink drop size and trajectory, the area around the printhead nozzles must be kept reasonably clean. Dried ink and paper fibers often stick to the nozzle plate and the cheek areas adjacent the nozzle plate, particularly on a wide tri-color pen, causing print quality defects if not removed. Wiping the nozzle plate only removes excess ink and other residue accumulated near the nozzle orifices.
In the past, the printhead wipers have typically been a single or dual wiper blade made of an elastomeric material. Typically, the printhead is translated across the wiper in a direction parallel to the scan axis of the printhead, so for a pen having nozzles aligned in two linear arrays perpendicular to the scanning axis, first one row of nozzles was wiped and then the other row was wiped. A revolutionary orthogonal wiping scheme was used in the Hewlett-Packard Company's DeskJet.RTM. 850C color inkjet printer, where the wipers ran along the length of the linear arrays, wicking ink from one nozzle to the next. This wicked ink acted as a solvent to break down ink residue accumulated on the nozzle plate. This product also used a dual wiper blade system, with special contours on the wiper blade tip to facilitate the wicking action and subsequent cleaning.
Some of the earlier systems wiped laterally across the orifice plate and across areas adjacent the orifice plate, smearing ink along the entire under surface of the printhead. Other orthogonal wiping systems wiped only the printhead orifice plate and ignored the "cheek" regions to the sides of the orifice plate. If left unwiped, these cheek regions accumulated ink particles or residue, which unfortunately then collected bits of dust, paper fibers and other debris. If ink residue from the orifice plate was smeared over the cheeks during a lateral wipe, this residue accumulated even more debris. This cheek debris was then moved across a printed image by the printhead, smearing the printed ink and degrading print quality.
Challenges were also faced in finding suitable capping strategies for the new pigment based inks, while also adequately capping the multi-color dye based printhead. Capping hermetically seals the area around the printhead nozzles to prevent drying or decomposition of the ink during periods of printer inactivity. Once again, the Hewlett-Packard Company's DeskJet.RTM. 850C color inkjet printer employed a unique multi-ridged capping system that adequately sealed the pigment based black pen. A spring-biased sled supported both the black and color caps, and gently engaged the printheads to avoid depriming them. A unique vent system comprising a Santoprene.RTM. cap plug and a labyrinth vent path under the sled avoided inadvertent deprimes, while also accommodating barometric changes in the ambient pressure.
While the radically new service station employed in the DeskJet.RTM. 850C printer addressed a myriad of problems encountered with the new pigment based inks, it had a couple of drawbacks. First, the various servicing features were mounted on a rotary tumbler system, which had a drive mechanism that some customers perceived as being somewhat noisy, having almost a low growling sound. Second, the tumbler assembly had quite a few parts, including a sophisticated priming system, so the service station required a series of intricate manufacturing steps for assembly. When given the opportunity to design a new service station for a new product, designers of the DeskJet.RTM. 850C service station teamed with their colleagues to improve on the earlier design, and their new preferred embodiment is described in the Detailed Description below.
Earlier printers also had another problem involving the carriage device that moves the printhead back and forth across the page during printing. To prevent damage to the carriage and printheads during transport, it is desirable to hold the carriage in a fixed location, rather than letting it thrash back and forth inside the printer. In the past, different types of locking mechanisms have been used to secure the carriage, but they typically required a separate mechanical locking lever that the operator had to move to secure the carriage to the chassis. Other earlier printers needed special packing material inside the printer to secure the carriage for shipment from the factory. For instance, in several designs the carriage was held in place using cardboard or foam packing material, adhesive tape, and the like. All this packing material then had to be removed by the consumer before printing could begin, and if some was missed, the printer could fail to print causing unnecessary frustration to the consumer.
For later consumer transport after these printers had been used, the frictional forces of the caps against the printheads was the primary mechanism that secured the carriage in place. Unfortunately, without the pens installed, or if the consumer forgot to engage the locking lever, the sheer mass of these carriages could cause them to slam back and forth into the sides of the printer during transport, possibly damaging the carriage, its drive mechanism, or its positional feedback mechanism. Thus, it would be desirable to have an automatic carriage locking mechanism that is "transparent" to the consumer, needing no user intervention to remove packing material upon initial purchase or to secure the carriage in place when the printer is turned off.